1. Field of the Invention
The present invention relates to a method of manufacturing a mask blank and a sputtering target for manufacturing a mask blank.
2. Description of the Related Art
In recent years, a semiconductor device has been demanded to be processed more finely. For this reason, an exposure wavelength to be used has come to be shorter than before. With respect of such a short exposure wavelength, various technical requirements are demanded for realizing such a mask blank more severely.
For example, a light translucent film (a halftone phase shift film) in a phase shift mask blank of a halftone type is employed to meet the demanded requirements from both aspects of a light transmittance and a phase shift amount for an exposure wavelength to be used.
With respect of such a short exposure wavelength, furthermore, it is also necessary to reduce a variation in a phase angle and a transmittance, which occurs among the mask blanks or in a mask blank plane itself, as much as possible in order to bring the mass production to the practical level. In a mask blank for a short wavelength, for example, an ArF or F2 excimer laser, a variation in a phase angle and a transmittance between blanks or in a plane in a mask blank for conventional i rays and a KrF excimer laser is great and a yield is also deteriorated. For this reason, an exact application cannot be carried out.
Under such a circumstance, a considerable change of the method or the apparatus has been further taken place in order to meet the demanded requirements apart from an extension of a conventional method or a conventional apparatus for manufacturing a mask blank.
More specifically, a mask blank to meet the demanded requirements is manufactured in a way such that films are formed by using a DC magnetron sputtering apparatus having the vacuum chamber in which a substrate holding table with a rotating mechanism, and a sputtering target opposed to the substrate in a position such that a center of the sputtering target is shifted from the central axis of the substrate in a predetermined angle to form a film while rotating a substrate with keeping a sputtering conditions in a constant state among a plurality of the substrates, such as disclosed in Japanese patent publication JP A 2002-90978. By this manufacturing method, it is possible to reduce the variation in the phase angle and the transmittance among the mask blanks or in a mask blank in the plane, which enables the mass production of a mask blank for a short wavelength, such as an ArF or F2 excimer laser, to be practical level.
In reflection of the reduction of the exposure wavelength, furthermore, the requirement for reducing a particle and a pinhole becomes more severely. In the mask blank for a short wavelength such as an ArF or F2 excimer laser, for example, it is also necessary to reduce the numbers of particles or pinholes as much as possible having the diameter that is larger than the half of the exposure wavelength in order to implement the practical use.
In order to meet such a demand, there is employed a manufacturing apparatus, more specifically, it might be a vacuum chamber of a DC magnetron sputtering apparatus which is comprised of a sputtering target having a target surface provided downward in the direction of a gravity, a substrate holder provided opposite to the target, and a shield disposed on the internal wall of the vacuum chamber in the same vacuum chamber using the above apparatus to form a mask blank which is manufactured by a film using a sputter-down formation method, such as disclosed in JP A 2002-90977.
With respect of the reduction in the exposure wavelength, both of the requirements that has been already mentioned above are demanded. In other words, reducing a variation in the phase angle and the transmittance among the mask blanks or in the mask blank in a plane, and suppressing the numbers of particles and pinholes are necessary for the mask blanks for a short wavelength such as ArF or F2 excimer laser to implement the practical use.
In order to manufacture a mask blank to meet these demanded requirements, there was employed a manufacturing apparatus combining both of the above structures together. That is, this combined structure presents a manufacturing apparatus which a DC magnetron sputtering apparatus, more specifically, it might be a vacuum chamber of a DC magnetron sputtering apparatus which is comprised of a substrate holding table having a rotating mechanism, a sputtering target opposed to a substrate in a position such that a center of the sputtering target is shifted from the central axis of the substrate in a predetermined angle where a target surface is provided downward in the direction of a gravity, and a shield provided on the internal wall of the vacuum chamber thereof, where approximately 100 mask blanks having light translucent films are continuously formed on the substrate by rotating the substrate with keeping a sputtering condition in a constant state between a plurality of substrates. As a result, however, there was a problem in that the particles with relatively large size (for example, a diameter of 300 nm or more) appear on the substrate. As the result of those particles being analyzed, it was found that most of the particles are constituted by In (indium) contain materials. This In is used as a bonding agent for bonding a target member to a backing plate in the sputtering target. For this reason, the source of generation of the particles might be the sputtering target. Although the particles of this type are rarely detected as the result of forming small number of the thin films, more the number of the formed films, more the number of the particles are generated. In this regard, in order to enhance the productivity of the mask blank, it is necessary to solve the problem of the generated particles.